PROTEINS 19 



alter all classifications without warning, but practically they may be 

 grouped under the headings of proteins, lipins, salts, and water, and 

 no attempt will be made to give here more tiian the most essential 

 features concerning each. 



PROTEINS 2 



In the last few years we have obtained something approaching a 

 scientific understanding of the chemical nature of this great group of 

 the most highly C()mi)lex bodies known to chemistry, although we 

 are still not in a position where it can be positively said just how the 

 various components of the molecule are united, or in exactly what 

 proportion ; and we are still farther", perhaps, from the point of 

 synthesizing a full-fledged protein molecule. But it is certain that 

 the problems regarding the underlying principles of the formation 

 and structure of the giant protein molecule are nearing solution. 

 Our information has been obtained almost exclusively through studies 

 of the products obtained by splitting up the proteins, for as yet 

 relatively little has been accomplished through synthesis. Proteins 

 can be decomposed by the action upon them of acids or alkalies in 

 various concentrations, by superheated steam, by digestive ferments, 

 and by bacteria. The products obtained in these different ways are 

 not all the same, for some substances may be formed by oxidation, re- 

 duction, decomposition, combination, or condensation of the various 

 products of simple cleavage, and it is necessary to distinguish between 

 the primary^ cleavage products (those which exist as radicals within 

 the molecule) and the secondary products (those not existing pre- 

 i'ormed in the molecule but formed by transformation of tlie primary 

 products). This can usually be done, and it is found that so far as 

 the primary products are concerned, it makes little difference which 

 method of cleavage (or hydrolysis, since in the splitting, water is com- 

 bined with the organic substances) is used. 



At first the proteins split up into compounds still possessing many 

 of the features of the typical protein molecule, such as albumoses and 

 peptones, and these bodies are then further resolved into simple sub- 

 stances, which are not aggregates of several smaller molecules as are 

 the proteins, and which can be obtained in pure crystalline forai. No 

 matter which method is used we find the process going through these 

 stages, and, as before mentioned, the primary crystalline products 

 obtained are practically the same quantitatively as well as qualita- 

 tively. Some methods, e. g., bacterial decomposition, however, lead in 

 the end to more profound or different decomposition of the cleavage 

 products into secondary substances. The similarity of the results ob- 



2 For the complete literature of this subject see :Mann's "Chemistry of the 

 Proteins." New York. 1000; "The Chemical Constitution of the Proteins," Plim- 

 mer, London, 1012: "The General Character of the Proteins," Schryver, London 

 1912: "Tlie Vegetable Proteins." Osbnrne, Tx)n(lon, 1010; (all the last tliree bein<r 

 in the series of "Monographs on .Biochemistry") . 



